Heat regenerator



Sept. 16, 1930. M, MARTIN. 1',776,162

HEAT REGENERATOR Filed April 9, 1923 2 hout-Shootl Pic-1.4. Fiaz.

' fhrenrar r v Mar Mk0 VIM r 'f p M. MARTIN KA HEAT REGENERATOR Sept. 16, 1930.

' Filed April 9, 1923 2 shoots-Shout 2 w. 0 I n e m l W// V//A Miclbaez Martin/fa y M Attorney Patented Sept. 16, 1930 PATENT OFFICE MICHAEL MARTINKA, OF RAKOSSZENTMIHALY, HUNGARY HEAT REGENERATOR Application filed April 9, 1923, Serial No.

The invention relates to heat regenerators, particularly but not exclusively to one for use in connection with internal combustion engine plants.

The invention will be best understood from the following description when read in the light of the accompanying drawings of several examples of the invention, while the scope of the invention will be more particu- 1olarly pointed out in the appended claims.

In the drawings Fig. 1 shows part of a regenerator;

Fig. 2 is a section on the line 22 of Fig. 1;

Fig. 3 is a cross section of a modified form 15 of the invention;

Fig. 3 is a perspective view showing the protubcrances;

. Fig. 3 is a similar View of a modified form of the protuhcranccs;

Fig. 4 shows a modified form of the regenerator in which the sections are formed of flat spirals; and

Fig. 5 shows a further modification;

Fig. 5 is a top view of a section of the re- 2 generator of Fig. 5 as it appears on line 5 5 of said figure;

Fig. 5 is a fragmentary sectional view the strips taken on line "5" of Fig. 5:

Fig. 5 is a similar view taken on line 5"-5 of Fig. 5, and

Fig. 5 is a similar view taken on line 55 of Fig. 5.

Heretotore it has been proposed to build heat regenera-tors comprising relatively closely spaced parallel metallic strips forming spaces through which cold and hot gases are caused alternately and reversely to flow for transferring the heat of the hot gas to the strips and afterwards from the strips to the cold gas.

I have found that in using metallic strips for the heat accumulating mass the losses may be decreased by dividing the regenerator into sect-ions separated from each other in the direction of gas flow by thin gas layers, and that the decrease in losses is proportional to the number of sections employed. For explanation of this result it may be noted, that if such a subdivided regenerator is traversed in regular time intervals alter- 631,023, and in Hungary April 20, 1922.

nately by hot and cold gases, it assumes a certain mean heat-equilibrium, in which the sections of the regenerator attain certain temperatures T T T The hot gas enters the regencrator on its hot side with a tem- 65 perature T which must be higher than that of the hottest section, say T =T AT and leaves the regencrator on its cold side with a temperature higher than that of the coldest section, say 'l l-AT On the contrary the cold gas which may have for sake of simplicity the same weight and the same physical properties, as the hot gas, enters the regen erator on the cold side with a temperature T lower than that of the coldest section, say T =T AT"... and leaves the regenerator on the hot side with a temperature lower than that of the hottest section. say T ATG. If the regencrator lrad no losses, the hot gas would be cooled by the regenerator from its initial temperature T to the lowest temperature T and the cold gas heated from its initial temperature T to the highest temperature T In reality the hot gas is only cooled from T to T +A T and the temperature drop from this latter temperature to T i. e. T -t A I,./ T -tA T' /=A T =A Tn is lost. It can he proved that if the temperature drop between two successive sections is the same throughout the regenerator, i. e. T -T 'l. .'l,,= T T,,=f. This temperature drop is given with good approximation by t= if n is the number of sections. and the before mentioned heat-loss of? the regenerator is with good approximation proportional with the temperature drop t, therefore with approximation inversely proportional with the number of sections. If, for example. the temperature of the hot gas is T =-=1000 (1. that of the cold gas T =2O C., and the number of sections n=48, the

temperature drop is t= =20.. The term perature of the hottest section is in this case T =980 C., that of the next one T =960 C., and so on, the temperature of all successive sections being 20 C. lower, than that of the foregoing one and the temperature of the 103 coldest section T =40 C. Instead of the heat corresponding to the temperature difference T ,,-T =980 C., the regenerator receives from the hot gas only the heat corresponding to the temperature difference T -T,, 960 and the heat corresponding to the difference T,, T,,=4020=20 C. is lost. The heat loss of the regenerator is therefore of the heat accumulated by the regenerator.

The space between the strips may be chosen preferably only to a fractionof a millimeter. In such a caseas it can be proved-very high coefficients of heat transmission can be obtained between the surface of the regenerator and the gases traversing the latter and what is more, independently from the speed of the gas flow. The latter can be chosen very small, so that the motion of the gas flow will be steady, i. e. takes places without turbulency, in which motion it is known that the friction-losses are much smaller than in a turbulent motion.

The subdivision of the regenerator into a great number of sect-ions has also with regard to the motion of gas fllow an advantageous influence. This, I explain, is due to the fact that the gas when entering the relatively narrow spaces of a section undergoes a. whirling motion, which causes an increase of the heat transmission above that amount, which would occur if the whirling motion did not take place. \Vhile the gas traverses the section, the whirling motion by and by will be calmed within the section into a lami nar motion, but the whirling motion takes,

place over again, when the gas enters the next section. So the whirling motion is renewed at the entrance of the gas in each section, consequently an increase of heat transmission proportional to the number of subdivisions is attained. By dividing the regenerator according to my invention into short sections in the direction of gas How and suitably spacing the sect-ions I am enabled to effect a whirling motion of the gas through the spaces throughout the length of the regenerator in the direction of flow because the whirling motion is recreated each time the gas flows into one 'of the sections.

Further by dividing the aegenerator into example, he of poor heat-conducting material and provided with grooves 2 into which are fitted metallic strips 1, the strips in each groove forming a section of the regenerator, the widths of the strips and spacing of the grooves being such as to provide spaces 5 between adjacent sections,'as viewed in Fig. 2.

In practice the hot and cold gases are caused to flow alternately in the direction of the arrows 6 and 7 (Fig. 2) through the gas conducting passages formed by the spaces 4' between the strips. The banks of metallic strips 1, as viewed in Fig. 1, form the sections heretofore referred to while the gas discharging from one section into the space .5 transversely intersecting the gas conducting passages, enters the next section with a whirling motion, as hereinbefore explained. As an example of the practice of the invention, but without limitation thereto, the strips 1 may have a thickness of about .1 millimeter and a width of from about 2 to 3 nfillimeters while the strips in'each section, as viewed in Fig. 1, maybe spaced from each other from .06 to .6 millimeter, and preferably not more than the latter. Preferably, but not necessarily, the spaces 5 may have a width of about that of the gas conducting passages, that is to say of from about .06 to .6 millimeter.

any suitable means may be provided for spacing the strips. For this purpose I have shown in Figs. 1 and 2 strips 4 which preferably are of insulating material, or, if desired. the strips 1 for this purpose may be provided with protuberances, say the ridges 8 shown in Fig. 3. If desired, to secure an approximate uniformity of the heat transmission c-oefticient the spacing between the strips 1 may be increased from one end of the regenerator toward the other in proportion to the increase of the absolute temperature of the gas flowing. I have found that the heat transmission coefficient is given by the formula where p denotes the heat-conductivity of the flowing gas and s the dimension of the space. As the heat-conductivity of a gas is increasing with the increase of temperature (nearly in proportion with the absolute temperature), the transmission coefiicient can be held constant by increasing the dimension 8 of the spacing in the same ratio as the heat-conductivity increases. In this Way a constant transmission coefficient is attained throughout the regenerator and consequentlya uniform utilization of the surface of the regenerator. v

A regenerator according to my invention can preferably be applied in caloric (hot-air or internal combustion) engines for the purpose of utilizing the heat still inherent in the hot working medium of the engine after it has performed its expansion in the hot working cylinder of the engine. After the expansion during the exhaust period of the engine the working medium exhausts through the regenerator entering the latter on its hot side with the still considerable final temperature of the expansion and being cooled within the regenerator to the temperature of the cold side of the latter, delivering thus the corresponding heat to the mass of the regenerator. During another period (the admission period) of the engine the returning working medium (inhot-air engines) or admitted fresh gases (ininternal combustion engines) in a comparatively cold state are introduced through the regenerator into the working cylinder and are heated when traversing the regenerator by the latter to the temperature of its hot side, thus taking up the heat delivered before by the exhaust gases.- It may be noted, that the regenerator attains always a certain heat equilibrium, characterized by the before mentioned mean temperatures T T T of its sections. While the hot gases flow through the regenerator, this mean temperature of the sectlons will increase with certain values T T T, and during the fiow of cold gases decrease with the same values. The temperatures of the sections fluctuate therefore regularly with said values around their mean temperatures corresponding to the mean heat equilibrium of the regenerator. The fluctuation of the temperature depends from the ratio of the heat received by the regenerator at one exhaust to the total heat accumulated in the mass of the regenerator. This ratio being in practical cases very small, thefluctuation of the temperatures of sections is only about 1-2 C. and can therefore be neglected.

In applying the regenerator to an internal combustion engine heat plant the regenerator conveniently may be built into the englne cylinder, as indicated in Fig. 5 in which 3 represents the cylinder head and 3 the cylinder walls. I have found that the deleteri ous effect on the engine efficiency of the increase of the clearance in the cylinder due to the presence of the regenerator may be compensated for by making the regenerator of decreasing cross-section from its hot end 12 to its cold end 11 as shown by Fig. 5 in substantially the same ratio as the absolute temperatures of the several sections of the heat regenerator decrease. This, I explain, is due to the fact that the specific volume of the as is a function of its absolute temperature. y so constructing the regenerator'the clearance effect may be compensated for without decreasing the capacity of the regenerator'and without increasing the surface heat losses and frictional resistance to gas flow. In practice I have found that excellent results may be obtained when the increase in total cross-sectional area from the cold toward the hot end is in the ratio of 3 to 1. Preferably the width of the passages alsois increased as above explained to attain a uniform heat transmission coefficient.

Conveniently, but not necessarily, the regenerator constructed according to Fig. 5 may be formed by making each section of a strip 10 coiled in the form of a flat spiral, the adjacent sections being spaced by wires.

As suitable for material for constructing the regenerator I have found that the strips may be made of quartz, nickel, cobalt, or alloys of nickel and cobalt. The sections exposed to the highest temperature may be made of strips compounded of granules of refractory metal oxide, or may be made of strips of quartz, while the subsequent sections proceeding toward the cold end of the regenerator may be made of nickel and, if desired, the sections subjected to the lowest temperature may be of copper or aluminum. When used with an internal combustion engine I have found that good results may be obtained with the sections subjected to the highest temperature preferably made of nickel.

Although I have described for purposes of illustration several examples of my invention, and it will be understood that I am not limited thereto and that wide deviations may be made without departing from the spirit of my invention.

I claim:

1. A heat regenerator, having a heat accumulating mass composed of a plurality of sections arranged in series in the direction of gas flow, said sections having narrow gas passages and said sections being of progressively increasing cross-section from-the cold to the hot end of said regenerator.

2. A heat regenerator, having a heat accumulating mass composed of a plurality of sections arranged in series in the direction of gas flow, said sections having narrow gas passages, said passages having progressively increased dimensions from the cold to the hot end of said regenerator and means to secure the increasing of said passages.

3. A heat regenerator, having a heat accumulating mass composed of a plurality of.

sections arranged in ceries in the direction of gas fiow, said sections composed of thin strips arranged edgewise in the direction of gas flow, the thickness of said stri s being substantially the same as the spacing etween said strips and means for spacing said sections.

4. A heat regenerator, having a heat accumulating mass composed of a plurality of sections arranged in series in the direction of gas flow, said sections composed of thin strips arranged edgewise in the direction of gas flow, the thickness of said strips being substantially the same as the spacing between said strips, the cross-section of said sections gradually increasing from the cold to the hot endof said regenerator, and means for spacing the successive Sections.

A heat rcgcnerator, having a heat accumulating mass composed of a plurality of sections arranged inserics in the direction of gas flow, said sections composed of thin strips arranged edgewise 1n the direction of gas flow. the thickness of said strlps being substantially the same as the spacing between said strips, said spacing gradually increasing from the cold end to the hot end of said regenerator, means for spacing the strips lying in the same section and means for spacing the successive sections.

6. A heat regencrator, having a heat accumulating mass composed of a plurality of sections arranged in series in the direction of 'as flow,'said sections composed of a plurality of thin straight parallel strips arranged edgewise in the direction of gas flow, means for spacing said straight strips, and means for spacing the successive sections.

In testimony whereof I affix my signature.

. MICHAEL MARTINKA. 

